Process for continuous casting of steel for making grain-oriented electrical sheet in strip or sheets

ABSTRACT

A process for the continuous casting of steel for the manufacture of grain-oriented electrical sheet, in strip or in sheets, wherein a primary cooling water and a secondary cooling water is used, characterized in that the primary cooling water is maintained at the minimum value compatible with not damaging the mould and with the attainment of a sufficient mechanical strength in the outer shell of the output slab.

1 United States Patent 1 Arbitrio et al.

[451 Apr. 17, 1973 PROCESS FOR CONTINUOUS CASTING OF STEEL FOR MAKINGGRAIN- ORIENTED ELECTRICAL SHEET IN STRIP OR SHEETS Inventors: PaoloArbitrio; Sandro Basevi; Alfredo Fornari; Antonio Sensi, all of Temi,Italy Assignees: Centro Sperimentale Metallurgico S.p.A.;, Terni SocietaPer LIndustria E LElettricita S.p.A., both of Rome, Italy Filed: Dec.28, 1970 Appl. No.: 102,038

Foreign Application Priority Data May 19, 1970 Italy ..50.8ll A/70 US.Cl ..l64/89, 164/128 Int. Cl. .,.....B22d 11/12 Field of Search 164/82,89, 283,

Primary Examiner-41. Spencer Annear Attorney-Young & Thompson 57]ABSTRACT A process for the continuous casting of steel for themanufacture of grain-oriented electrical sheet, in strip or in sheets,wherein a primary cooling water and a secondary cooling water is used,characterized in that the primary cooling water is maintained at theminimum value compatible with not damaging the mould and with theattainment of a sufficient mechanical strength in the outer shell of theoutput slab.

6 Claims, No Drawings PROCESS FOR CONTINUOUS CASTING OF STEEL FOR MAKINGGRAIN-ORIENTED ELECCAL SHEET IN STRIP OR SHEETS The present inventionrelates to a continuous casting process for silicon steel suitable tomake grain-oriented electrical sheet in strip or sheet form.

It is known that for making the silicon steel for magnetic uses, theentire transformation cycle of the semifinished product is tied to a setof critical conditions which must be complied with, as far as both theteeming of steel ingots (weight, size and shape of the ingot) and thesubsequent operations of hot and cold plastic working, and the thermaltreatings, are concerned. It is also known that these criticalconditions are strictly connected to one another, whereby if one or moreof the aforesaid conditions are changed, particularly the conditionsconcerning the ingot making, it will no more be possible to control thereproducibility of the critical features of the final product. By thetrend recently revealed of adopting the continuous casting also for thesilicon steels, the problems connected to the metallurgical conditionscharacterizing the solidification of a conventionally cast ingot in pigiron ingot mold undergone a radical change whereby the manufacturedproducts of silicon steel obtained by continuous casting will show alargely heterogeneous behavior, affecting the magnetic features of thefinished product.

In fact, the influence shown by the composition, the dimensions andthedistribution of the impurities in the grain orientation process isknown; when the additive selected for this purpose is the sulphur, it isobserved that due to the particular solidifying conditions occurring inthe continuous casting, the distribution, composition and shape of thesulphides is such that a Bauman etching made on a continuous cast slabgives an almost invisible image of the distribution of said sulphides,contrarily to the result obtained from the Bauman etchings of the slabs,obtained from an ingot.

It is necessary, therefore in the silicon steel continuous casting, toachieve certain conditions which are rather critical.

The purpose of the present invention is that of speci fying the criticalvariable values intervening during the continuous casting of saidsilicon steels, so as to attain a final product having an optimum andreproducible quality.

Following long tests on a continuous casting plant, said criticalconditions, forming the subject matter of the present invention havebeen defined: said critical conditions, if respected, allow to obtainslabs which, when submitted to conventional subsequent working cycles,will originate a final product having magnetic features at leastcomparable to those obtainable by using conventional ingot cast steel.For instance, for a sheet 0.35 mm thick, the loss measured at 50 Hz and15,000 Gauss is less than or equal to 1.11 Watt/kg and the permeabilitymeasured at Oersted is greater than, or equal to, 1790 Gauss/Oersted.

According to the present invention, the molten steel to which allsubstances capable of imparting to it the desired magnetic features havebeen added, is stirred within the ladle, by blowing argon through it sothat it will have at the start of the casting a temperature cornprisedbetween 1,560C and 1,600C, preferably a temperature comprised between1,560C and 1,570C. The

casting is made by means of submerged nozzles from the ladle to thetundish and therefrom to the molds, and the molten metal is protected bya slag consisting essentially of CaO, SiO A1 0 CaF-Z. The molten metalis cast so as to have a feeding speed of the slab included between 700and 1,000 kg/min, and for slabs of 900 X 140 mm the feed speed is about800 ltg/rnin.

The primary cooling water of the continuous casting plant has theminimum possible flowing rate so as to ensure the sealing of the moldand a sufficient mechanical strength of the solidified outer shell ofthe slab in order to allow for its extraction with no break. The primarycooling water has a flow rate comprised between 2.8 and 4 cu.m/ton ofsteel; for a slab of 900 X 140 mm the water flow rate must be notgreater than 3.6 cu.M/ton of steel.

The secondary cooling water of the continuous casting plant, sprayedalong a variable number of zones will have such a flow rate as to allowfor the minimum possible removal of heat in order to have at theextraction rolls of the machine, the cross sectional area of the slabentirely solidified. Said water flow rates are comprised between 0.16and 0.24 cutm/ton of steel in the first of said zones, while in theother zones the rate will be included between 0.04 and 0.10 cum/ton.

EXAMPLE A heat of 50 tons of steel having the following analysis: C0.04, Si 3.10, S 0.022, P 0.015, Mn 0.065, Cr 0.08, Ni 0.10, Mo 0.02, Cu0.10 Al less than 0.005, the balance being iron, is brought to thecontinuous casting plant after stirring by Ar, at a 1,580C temperature,then the steel is cast in the copper mold (1,500 mm high, 900 mm wide,140 mm thick) and after the mold has been filled, itis covered byprotecting slag. The casting is started at a rate of 840 kg of steel perminute. The flow rate of the primary cooling water is adjusted at 3.6cum/ton. The secondary cooling is adjusted as follows: 1st zone 0.2cum/ton, 2nd zone and following four zones: 0.08 cum/ton,

The so obtained slabs are stacked and left to slowly cool in still air.After working the final sheet has the features as follows: 0.35 mmthick, loss at 50 Hz and 15,000 Gauss equal to 0.95 watt/kg andpermeability at 10 Oersted equal to 1810 Gauss/Oersted.

The sulphur contents of the continuously cast steel according to thepresent invention equals percent by weight of the sulphur contained :inthe corresponding type of the ingot-cast steel. The carbon contents ofthe continuously cast steel according to the process of the presentinvention is higher by 0.01 percent by weight than that of thecorresponding type of steel conventionally teemed into ingot molds.

Having thus described the present invention, what is claimed is:

l. A process for the continuous casting of silicon steel for themanufacture of grain-oriented electrical sheet and strip, comprisingcasting silicon steel into a continuous casting mold at a temperaturebetween 1,560C. and 1,600C., cooling the mold by passing through themold primary water at a flow rate less than 3.6 cubic meters per ton ofsteel, spraying on the slab that emerges from the mold secondary coolingwaterin a first zone at a rate between 0.16 and 0.24 cubic meter per tonof steel, and spraying on said slab which 5. A process as claimed inclaim 1, in which the steel contains sulphur in an amount about percentof the sulphur contained in the corresponding type of steelconventionally teemed into ingot molds.

6. A process as claimed in claim 1, in which the steel contains carbonin an amount higher by about 0.01 percent by weight than that of thecorresponding type of steel conventionally teemed into ingot molds.

2. A process as claimed in claim 1, in which said silicon is about 3.1percent by weight.
 3. A process as claimed in claim 2, in which thesteel contains about 0.04 percent by weight carbon.
 4. A process asclaimed in claim 1, in which said temperature is between 1,560*C. and1,570*C.
 5. A process as claimed in claim 1, in which the steel containssulphur in an amount about 90 percent of the sulphur contained in thecorresponding type of steel conventionally teemed into ingot molds.
 6. Aprocess as claimed in claim 1, in which the steel contains carbon in anamount higher by about 0.01 percent by weight than that of thecorresponding type of steel conventionally teemed into ingot molds.